Field of the Invention
The present invention relates to a feeding apparatus and an image forming apparatus.
Description of the Related Art
An image forming apparatus such as a printer and a copying machine conventionally includes a feeding apparatus for feeding sheets one by one. As a feeding apparatus, a configuration such as illustrated in FIGS. 10A and 10B is known, which includes a stacker 14 serving as a sheet stacking unit and a feed roller 20 serving as a feeding unit for feeding sheets on the stacker 14.
To stabilize sheet feeding conditions when using (consuming) sheets S on the stacker 14 for printing, the feeding apparatus includes a sheet surface detection mechanism for detecting the height of the topmost surface of the sheets S on the stacker 14. Among known configurations of the sheet surface detection mechanism, there is a mechanism using a sheet surface detection member 40 which makes contact with the top surface of a sheet as illustrated in FIGS. 10A and 10B.
Deterioration of the feed roller 20 due to wear can lower the feeding performance of the feeding apparatus. Japanese Patent No. 4612893 discusses a feeding apparatus in which a feed roller 20 is configured to be detachably attached to the main body of the feeding apparatus so that the feed roller 20 can be replaced on a regular basis. According to the feeding apparatus discussed in Japanese Patent No. 4612893, the feeding performance (frictional force and outer diameter) of the feed roller 20 can be maintained above a certain level, and feeding failures (non-feeding and multi feeding) can be prevented from occurring.
However, the configuration in which the feed roller 20 is replaced when it is worn to a certain degree or more, like the feeding apparatus discussed in Japanese Patent No. 4612893, has the following problem.
Replacing the feed roller 20 refreshes and keeps the performance of the feed roller 20 itself in a good condition. However, the sheet-contacting portion of the sheet surface detection member 40 which is constantly in contact with the top surface of the sheets S also wears off depending on its durability. As a result, there can occur a problem that the topmost surface of the sheets S on the stacker 14 cannot be properly detected or controlled. The problem will be described below with reference to FIGS. 10A, 10B, 11A, and 11B.
FIGS. 10A and 10B illustrate a case where both the feed roller 20 and the sheet surface detection member 40 are new ones. In such a configuration, the stacker 14 stops its lift up in a position where the topmost sheet S on the stacker 14 pushes up the sheet surface detection member 40 by a predetermined amount. FIG. 10A is a sectional view of the feeding apparatus. FIG. 10B is an enlarged view of the vicinity of the feed roller 20. For favorable feeding performance, the feeding apparatus is configured such that the leading edge of the sheet S is appropriately guided to a nip portion between a conveyance roller 21 and a separation roller 27.
FIGS. 11A and 11B illustrate the state where the feeding of sheets S is repeated, so that the feed roller 20 and the sheet surface detection member 40 are worn out, and then only the feed roller 20 is replaced. As illustrated in FIG. 11B, if the sheet surface detection member 40 alone is worn out (Δh in the diagram), the direction of the leading edge of a sheet S on the stacker 14 can be different from when the sheet surface detection member 40 is a new one. In such a state, the sheet S may fail to be successfully fed into the nip portion between the conveyance roller 21 and the separation roller 27. This sometimes results in damage to the leading edge of the sheet S, or even a feeding failure (non-feeding) of the sheet S, etc.